There are many applications, including photographic processing, where processing chemicals are supplied in liquid form in containers. When such a chemical is emptied from its container into a processing apparatus air will normally pass into the container naturally to replace the liquid so that the container is eventually filled with air. If the chemical is subsequently to be returned to the container provision must be made to accommodate any air which remains trapped within the container or which is entrained within the chemical as it is pumped back into the container or provision must be made to remove the air.
This is particularly important in the case of photographic processing chemicals such as developer, fixer or the like where the presence of air in the container for a processing chemical will cause oxidization and degradation of the chemical. Various methods are therefore used in order to try and exclude air from the container for a photographic processing chemical. It is not unknown, for example, for a lighted spill to be used in order to burn off the oxygen in a bottle used as a container for a photographic processing chemical. This is, however, far from an ideal solution. Another way in which the problem has been addressed is to provide a manually operated valve or vent tap in that region of the container which is located uppermost when it is in use so that the interior of the container may be connected to atmosphere to allow any air present in the container to escape as the container is filled with chemical. The construction of a container incorporating a manually operable vent of this type is, however, rather complex and therefore expensive and the vent must be operated manually. A container of this type is therefore not particularly suitable for use in an automated processing apparatus.
A further approach to the problem of excluding air from a container for a photographic processing chemical has been to design the container as a flexible "bag" or package which, when charged with a processing chemical, may be squeezed by hand in order to expel any air present in the container before the container is sealed closed. Again however this arrangement is really only suitable for manual use and where the processing chemicals are returned to their containers on an infrequent basis.
In addition a flexible foil package, i.e. a package formed from a thin membrane, is known which has only a single connection by way of which the chemical is introduced into and removed from the package and the flexible package collapses when the chemical is extracted and the pressure within the container decreases. Such a design has the limitation of only being of particular use when it is oriented with its connection located uppermost because otherwise air can become trapped in the package over successive cycles of operation and that air trapped in the package can eventually prevent the return of all of the processing chemical to the container. This can result in exhausted processing chemicals being left in a processing apparatus, which is particularly undesirable insofar as a photographic processing apparatus is concerned because any contaminated or exhausted solution left in a processing tank of a photographic processing apparatus will contaminate a fresh supply of processing chemical introduced into that tank.